Plasma membrane fluidity and heterogeneity of polymorphonuclear leukocytes (PMN) were investigated in seven children with primary ciliary dyskinesia (PCD) and 17 healthy controls. Membrane fluidity and heterogeneity were studied by measuring the steady state fluorescence anisotropy and fluorescence decay of 1-(4-trimeth-ylammoniumphenyl)-6-phenyl-1,3,5-hexatriene (TMA-DPH) incorporated into PMN plasma membrane. Our results show an increase in membrane fluidity at the surface level of PMN from patients with PCD. Distribution analysis of TMA-DPH lifetime values indicate an increase in membrane heterogeneity in subjects with PCD. The observed changes in the physicochemical properties of the membrane could lead to alterations in the function of PMN from children with PCD.